Scientists Warn to Expect More Weather Extremes

Torrential rains and widespread flooding in Texas have brought relief from a yearslong drought to many parts of the state. Such unpredictable and heavy rains are a big part of what climate scientists say that many Texans can expect in years to come.

The relief has come at a great cost. The death toll from storms across the state and Oklahoma has reached at least 19, by some estimates, and the property damage is so extensive that Gov. Greg Abbott of Texas has declared some 40 counties disaster areas.

It was not long ago that the state was dealing with a searing drought. In 2011, the drought was so pronounced that the governor then, Rick Perry, proclaimed three days in April “days of prayer for rain in Texas.” Parts of the state began to see the drought ease by 2012, but much of it has remained parched.

Now, Texans are more likely to be asking for divine intervention to provide a little sunshine. Reservoirs that had reached historically low levels are brimming, or at least rising fast. The water level at Lake Travis near Austin rose nearly 24 feet in the last week. It was just 34.2 percent full a year ago; today it is 65.5 percent full. Across the state, reservoirs have collected about eight million acre feet of water, rising to 82 percent full from 73 percent full in a month, according to the Texas Water Development Board.

Texans are no strangers to extreme weather, said Katharine Hayhoe, a climate change researcher at Texas Tech University and an author of the 2014 United States National Climate Assessment. “It’s famous for floods and drought, hurricanes and tornadoes, dust storms and ice storms,” she said. “Climate change is not causing these events — they’ve always happened naturally. But climate change is exacerbating these events.”

She noted that the enormous building boom that Texas has enjoyed in recent decades has led to greater problems with water runoff and higher costs of storm damage. “The choices we’re making today are actually increasing our risk,” she added.

Bill Nye, a popularizer of science and a climate activist, came under attack this week for talking about the rains as a climate-change event; some pointed out that in 2012, he suggested that the Western drought “is absolutely consistent with the mathematical models and predictions associated with climate change.”

Yet different parts of the country, and different parts of the country-size state of Texas, can expect different kinds of weather extremes. Severe rainstorms are consistent with the physics of a warming world, with plenty of moisture evaporating off the oceans, Professor Hayhoe noted — especially in the eastern part of the state near the Gulf of Mexico, where things tend to be wet and getting wetter. But the western part of the state is more like the American Southwest, and drier.

John W. Nielsen-Gammon, Texas’ state climatologist and a professor at Texas A & M University, said that Texas weather was heavily influenced by long-term weather phenomena, including El Niño and natural variations of temperatures in both the Atlantic and Pacific oceans.

For now, he said, the slight rise in sea surface temperatures may have added 4 or 5 percent to the recent rainfall, but the longer-term trends for much of the state call for “a decrease of a few percent” in rainfall. It could take many decades, he said, before the effects of warming become a more important factor in the state’s weather than the natural variability.

Andrew E. Dessler, a climate researcher at Texas A & M, compared the question of climate change and weather to trying to figure out which of Barry Bonds’s home runs were caused by his steroid use.

“You know statistically some of them were, but you don’t know which ones,” he said. “Almost certainly, it would have rained a lot even without climate change — but it’s possible climate change juiced it, added a little bit.”

A version of this article appears in print on , on Page A18 of the New York edition with the headline: Scientists Warn to Expect More Weather Extremes . Order Reprints | Today’s Paper | Subscribe